1. Field of the Disclosure
The present disclosure relates to an organic light-emitting diode (OLED) display device, and more particularly, to an organic light-emitting diode (OLED) display device having sub-pixels with four colors.
2. Discussion of the Related Art
A cathode ray tube (CRT) has been widely used as a display device for a long time. However, lately, flat panel displays, such as a plasma display panel (PDP), a liquid crystal display (LCD), and an organic light-emitting diode (OLED) display device, have been developed as a display device with which can replace the CRT, and are widely used.
Among flat panel displays, the OLED display device which is a self-luminous device, can be manufactured as a light-weighted and slim product since it requires no backlight, unlike the LCD which is a non-emissive device.
Also, the OLED display device is excellent in view of a viewing angle and a contrast ratio, advantageous in view of consumption power, allows DC low voltage driving, and has a high response rate. In addition, since the internal material of the OLED display device is a solid, the OLED display device is resistant against external impacts, and has a wide range of usable temperature.
In particular, since the OLED display device can be manufactured through a simple process, manufacturing costs are lower than those of the LCD.
The OLED display device is a self-luminous device that emits light through organic light-emitting diodes, and the organic light-emitting diodes emit light through organic electro luminescence.
FIG. 1 is a band diagram of an OLED display device 10 that emits light through organic electro luminescence.
As shown in FIG. 1, the OLED display device 10 includes an anode electrode 21, a cathode electrode 25, and an organic light-emitting layer interposed between the anode electrode 21 and the cathode electrode 25. The organic light-emitting layer includes a hole transport layer (HTL) 33, an electron transport layer (ETL) 35, and an emission material layer (EML) 40 interposed between the HTL 33 and the ETL 35.
In order to improve luminous efficiency, a hole injection layer (HIL) 37 is interposed between the anode electrode 21 and the HTL 33, and an electron injection layer (EIL) 39 is interposed between the cathode electrode 25 and the ETL 35.
In the OLED display device 10, if positive (+) and negative (−) voltages are applied to the anode electrode 21 and the cathode electrode 25, respectively, the holes of the anode electrode 21 and the electrons of the cathode electrode 25 are transported to the emission material layer 40 to generate excitons, and when the excitons return to the ground state from the excited state, light is generated and emitted in the form of visible light by the emission material layer 40.
Meanwhile, lately, studies into a full color OLED display device are actively being conducted. The emission material layers 40 of a plurality of organic light-emitting layers represent red, green, and blue colors.
A full color OLED display device can control its color reproduction range and life span according to the kind of blue organic material.
If a blue emission material layer is made of a deep blue organic material, the deep blue organic material has an excellent color reproduction range, but has a shorter life span and lower luminous efficiency than a sky blue organic material.
Sky blue organic material is excellent in view of life span and luminous efficiency, compared to deep blue organic material, but has a relatively narrow color reproduction range.
Accordingly, in order to efficiently use a blue emission material layer, an OLED display device 10 with four color organic emission layers including a deep blue emission material layer and a sky blue emission material layer in a pixel, has been introduced.
Meanwhile, the OLED display device 10 with the four color organic emission layers has low process efficiency since the four color organic emission layers should be individually formed by vacuum thermal evaporation.
That is, in the OLED display device 10, the remaining components except for the anode and cathode electrodes 21 and 25, that is, organic emission layers, such as the HIL 37, the HTL 33, the emission material layer 40, the ETL 35, the EIL 39, etc., are formed generally through vacuum thermal evaporation.
Specifically, vacuum thermal evaporation for forming the emission material layer 40 is performed by placing an organic material with a desired color in a deposition source (not shown) having a discharge opening, heating the deposition source in a vacuum chamber (not shown) to evaporate the organic material, discharging the evaporated organic material through the discharge opening, and then depositing the discharged organic material on a substrate (not shown).
Vacuum thermal evaporation can form an emission material layer 40 with one color when it is once performed, and requires a long process time. Accordingly, manufacturing time of the OLED display device 10 increases as the number of vacuum thermal evaporation operations increases. Also, since various colors of organic materials are needed, the cost of materials increases and process efficiency is low.